This application is based upon and claims benefit of priority of Japanese Patent Applications No. 2001-131604 filed on Apr. 27, 2001, No. 2001-152771 filed on May 22, 2001 and No. 2001-277184 filed on Sep. 12, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an air-conditioner for use in an automotive vehicle in which an internal combustion engine mounted thereon is automatically stopped when the automotive vehicle comes to a temporary halt at an intersection or the like.
2. Description of Related Art
Recently, an automotive vehicle having a so-called idle-stop device, which automatically stops an engine when the vehicle comes to a temporary halt at an intersection or the like for saving fuel consumption, is being introduced in the market. Since a compressor of an air-conditioner mounted on such a vehicle is driven by the engine, operation of the compressor is also stopped when the engine is temporarily stopped. If the compressor comes to a halt, the air-conditioner does not perform a desired function.
JP-A-2000-127753 proposes an air-conditioner system which solves the above problem. In this system, a sub-compressor which is driven by an electric motor during a period in which the main compressor is not driven by the engine is connected in parallel to the main compressor. In this manner, the air-conditioner is able to continue its operation during such a period. Since sub-compressor is connected in parallel to the main refrigeration circuit in this system, refrigerant mixed with lubricant circulating in the main refrigeration circuit tends to enter into a sub-circuit including the sub-compressor when the main compressor is operated and the sub-compressor is not operated. The refrigerant entered into the sub-circuit still remains therein when the operation of the main compressor resumes. Therefore, an amount of refrigerant including lubricant becomes short in the main refrigeration circuit, and the main compressor cannot be properly lubricated. This results in not only insufficient cooling ability of the air-conditioner but also reduction in an operable life of the main compressor.
Since the main compressor and the sub-compressor are alternately operated, the same problem also occurs in the sub-circuit including the sub-compressor. The refrigerant mixed with lubricant enters into the sub-circuit or the main refrigeration circuit and remains therein is called xe2x80x9csleeping refrigerantxe2x80x9d. In order to reduce the amount of the sleeping refrigerant, the above-mentioned JP-A-2000-127753 also proposes to dispose one-way check valves in both the main circuit and the sub-circuit, or to install valves switching flow directions of the refrigerant at junctions connecting the sub-circuit to the main refrigeration circuit. If one-way check valves are used, four of them are necessary to control the flow directions of the refrigerant. This makes the air-conditioner expensive and complex, and further makes it difficult to add the sub-circuit including the sub-compressor to the existing main refrigeration circuit.
The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an improved automotive air-conditioner having a sub-compressor driven by an electric motor, and more particularly to reduce an amount of refrigerant remaining both in a main refrigeration circuit and in a sub-circuit of such an air-conditioner without making its structure complex. Another object of the present invention is to improve durability of the compressor by providing the compressors with sufficient lubrication. Another object of the present invention is to provide an air-conditioner in which the sub-circuit including the sub-compressor is easily added to an existing refrigeration circuit. Yet another object of the present invention is to provide an air-conditioner having a sub-compressor which is driven quietly during a vehicle is not driven.
The air-conditioner of the present invention is mounted on an automotive vehicle which has a so-called idle-stop mechanism. An internal combustion engine for driving the vehicle is stopped every time the vehicle temporarily stops at an intersection or the like for saving fuel consumption.
The air-conditioner includes a main refrigeration circuit and a sub-circuit. The main refrigeration circuit is composed of a main compressor, condenser, an expansion valve and an evaporator, all connected in series. The main compressor and the evaporator is connected through a low pressure tube, and the main compressor and the condenser is connected through a high pressure tube. A first junction and a second junction are formed in the low pressure tube and in the high pressure tube, respectively. The sub-circuit is composed of a sub-compressor and inlet and outlet pipes connected to the sub-compressor. The sub-compressor is connected in parallel to the main compressor by connecting the sub-circuit between the first and the second junctions.
The main compressor is driven by the engine while the engine is in operation, and the sub-compressor is driven by an electric motor while the engine is not in operation. Thus, the air-conditioning ability of the air-conditioner is maintained at a required level even when the engine is not in operation. The capacity of the sub-compressor is smaller than that of the main compressor, and the pipe size in the sub-circuit is made smaller than that of the main refrigeration circuit.
Because the sub-compressor is not in operation while the main compressor is in operation, refrigerant mixed with lubricant circulating in the main refrigeration circuit enters into the sub-circuit and retained therein. This causes shortage of refrigerant in the main refrigeration circuit. On the other hand, the refrigerant may be retained in the main refrigerant circuit while the main compressor is not in operation, causing refrigerant shortage in the sub-circuit.
To prevent the refrigerant from entering into the sub-circuit and being retained therein, the inlet pipe and the outlet pipe of the sub-circuit are branched out upwardly from the first and the second junctions. This structure suppresses refrigerant communication between the main refrigerant circuit and the sub-circuit. The inlet pipe of the sub-compressor may be branched out from the first junction first downwardly and then upwardly. In this manner, the refrigerant held in the downwardly branched out portion is sucked into the sub-circuit when the sub-compressor resumes its operation thereby to sufficiently lubricate the sub-compressor.
The sub-compressor and the electric motor for driving the sub-compressor may be contained in an unitary package. The unitary package is mounted on the vehicle via a shock absorbing member to alleviate vibration transferred from the vehicle to the sub-compressor. Looped or cranked portions may be formed in the inlet and the outlet pipes of the sub-compressor, respectively, to alleviate vibration transferred from the sub-compressor to the main refrigeration circuit. The sub-circuit composed of the sub-compressor and the inlet and outlet pipes is easily added to the main refrigeration circuit, e.g., to an existing refrigeration circuit.
Alternatively, the electric motor for driving the sub-compressor may be controlled by an electronic controller to return the refrigerant remaining in the sub-circuit to the main refrigeration circuit, or vice versa. The sub-compressor may be driven for a short predetermined period when the main compressor is in operation. In this manner, the refrigerant retained in the sub-circuit while the sub-compressor is not in operation is returned to the main refrigeration circuit. The sub-compressor may be intermittently and repeatedly operated for that short predetermined period with a certain interval in order to sufficiently return the refrigerant to the main refrigeration circuit. The sub-compressor may be driven for a short predetermined period immediately after the main compressor resumes its operation to lubricate the main compressor. The predetermined short period may be changed according to operating conditions of the engine or a required heat load of the air-conditioner. In case the refrigerant is retained in the main refrigerant circuit, the sub-compressor may be driven for a short time immediately before the sub-compressor resumes its operation. In this manner, the refrigerant retained in the main refrigerant circuit is returned to the sub-circuit to lubricate the sub-compressor.
Alternatively, a compressor having a variable capacity may be used as the main compressor. The capacity is increased to a level higher than a level for attaining a required cooling ability for a predetermined period of time immediately after the main compressor resumes its operation. In this manner, the refrigerant retained in the sub-circuit is instantly sucked into the main refrigerant circuit. The capacity may be increased up to a maximum capacity of the variable-capacity compressor. The capacity increase may be intermittently repeated during a period in which the variable-capacity compressor is in operation.
According to the present invention, the refrigerant mixed with lubricant is prevented from entering into the circuit which is not in operation by a simple and inexpensive structure in the air-conditioner. Both the main compressor and the sub-compressor are sufficiently lubricated, and thereby durability of the compressors is improved. The sub-circuit including the sub-compressor is easily mounted on the vehicle while suppressing noises generated by the sub-compressor. Further, the refrigerant retained in the sub-circuit or the main refrigeration circuit is efficiently returned to right positions requiring the refrigerant.